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Plants that act like people

Aside from an active social life, plants display a whole range of other human-like behaviours. New Scientist looks at plants that can choose their mate, others that cry out for help and some that can even fake an illness.

Choosing a mate

Many plants avoid pollen from other species by forming special relationships with particular pollinators, such as birds, ants and insects. But tobacco plants (from the Solanaceae family) are even more choosy.

Their self-incompatibility system allows them to reject the pollen of close relatives, which would produce weaker inbred plants. Exactly how this works is still unknown.

False lure

To improve its chances of pollination, the fly orchid (Ophrys insectifera) tricks male flies into mating with it. As well as looking like an insect, the orchid releases a scent that mimics the sexual pheromones of female flies. Then, when the hapless male attempts to mate with the flower, it pollinates the orchid.

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Phoney war

The passion fruit plant (Passiflora) uses deception to deter Heliconius butterflies from laying their eggs on its leaves. This isn't done simply out of spite: the eggs hatch into caterpillars that can severely damage or even kill the plant.

Its sophisticated defence mechanism involves producing growths called stipules that mimic mature butterfly eggs. The deception works because, to give their offspring the best possible chance of survival, butterflies tend to avoid laying their eggs on a leaf that already has eggs on it.

(Image: Altrendo Nature/Getty)

Faking illness

The elephant's ear Caladium steudneriifolium is prone to infestations of mining moth larvae: once hatched, the caterpillars eat their way through its leaves. To prevent this, plants can feign illness, displaying a white variegation pattern on their leaves which resembles recent larval damage. Preferring to exploit a healthy plant, the moths lay their eggs elsewhere.

The leaf on the left shows real predation, whereas the one on the right has been variegated by the plant to mimic it.

(Image: Sigrid Liede-Schumann/department of plant systematics, University of Bayreuth, Germany)

Timidity

The appropriately named touch-me-not plant (Mimosa pudica) shies away from any physical interaction. A gentle touch is all it takes for the narrow fern-like leaves of the plant to instantly fold together, making the whole leaf stalk droop.

The touch-induced movement is thought to be a defence mechanism: the plant gradually returns to normal after about half an hour, when the coast should be clear.

Neighbourhood watch

When leaves of the sagebrush Artemisia tridentata are clipped and damaged by insects, they release a chemical SOS alerting their neighbours to danger. Nearby tobacco plants then pick up the warning and in response they release their own chemicals to prevent insect attacks.